Food and drink products and other perishable items are often packaged in tubular containers which are sealed at both ends. These tubular containers typically include at least one structural body ply and are formed by wrapping a continuous strip of body ply material around a mandrel of a desired shape to create a tubular structure. The body ply strip may be spirally wound around the mandrel or passed through a series of forming elements so as to be wrapped in a convolute shape around the mandrel. At the downstream end of the mandrel, the tube is cut into discrete lengths and is then fitted with end caps to form the container.
Tubular containers of this type typically include a liner ply on the inner surface of the paperboard body ply. The liner ply prevents liquids such as juice from leaking out of the container and also prevents liquids from entering the container and possibly contaminating the food product contained therein. Preferably, the liner ply is also resistant to the passage of gasses, so as to prevent odors of the food product in the container from escaping and to prevent atmospheric air from entering the container and spoiling the food product. Thus, the liner ply provides barrier properties and the body ply provides structural properties.
Conventional liner plies are most often made of aluminum foil which has good barrier properties and also has advantageous strength properties. In particular, the liner is wound onto the mandrel prior to the winding of the body ply and must be sufficiently strong and stiff to be independently wound on the mandrel without stretching or wrinkling. Because of the support provided by the foil layer of the liner, such liners are known as "supported" liners.
One or more polymeric layers are normally adhered to the foil to further improve the barrier properties of the liner and it is sometimes the case that the foil layer is not necessary for barrier properties but is included in the liner only to provide support. Such foils are expensive and thus it is desired to provide an "unsupported" liner having the requisite barrier properties without the aluminum foil layer. However, because of the problems associated with winding an unsupported liner on the mandrel, such as stretching, creasing or other misshaping of the liner, it has not been commercially feasible with conventional winding apparatus and methods to manufacture a container having an unsupported liner ply.
In addition, the aluminum foil layer typically includes a kraft paper backing for allowing the foil layer to be adhered to the paperboard body ply. Aqueous based adhesives (or "wet adhesives") are preferably used to adhere the liner ply to the body ply because solvent based adhesives have become disadvantageous in light of various environmental concerns. However, it has heretofore been difficult to get the aqueous adhesives to stick to the smooth and impervious surface of the aluminum foil layer. Accordingly, a kraft paper backing has been preadhered to the foil layer so that the liner can be adhered to the paperboard body ply with wet adhesives. However, the kraft paper adds further cost and thickness to the liner.
The liner ply is also sealed to itself along a helical seam which is typically slightly offset from the helical seam of the body ply. Wet adhesives have typically not been able to adhere directly to the foil layer as discussed above, and thus the liner ply seam is formed with an "anaconda" fold, wherein the overlying edge of the liner ply is folded back on itself and adhered to the underlying edge. The anaconda fold allows the polymeric layers on the surface of the foil layer to be heat sealed together. Alternatively, a hot melt adhesive can be used to seal the anaconda fold of the overlying edge of the liner ply to the underlying edge. An additional advantage of the anaconda fold is that the edge of the kraft paper is not exposed to the interior of the container and thus liquids in the container will not be absorbed by the kraft paper. An example of such a fold is illustrated in U.S. Pat. No. 5,084,284 to McDilda, et al.
Anaconda folds are undesirable, however, because of their increased thickness. The thickness of an anaconda fold seam is equal to three thicknesses of the liner ply and poses difficulties when attempting to hermetically seal the ends of the tubular container. Specifically, the ends of the tube are often rolled outwardly after being cut so as to form a rolled circular bead or flange on one or both ends of the tube and then end caps or covers are sealed to the bead with an adhesive sealant or compound. However, in the area where the thick anaconda fold seam forms a portion of the edge surface, the end surface of the bead or flange can be substantially non-planar thus forming hill-like and/or valley-like irregularities. Accordingly, an extra amount of adhesive sealant must be applied to the edge surface at least in the area of the anaconda fold seam to fill the discontinuities and hermetically seal the tubular container. The additional application of adhesive sealant is disadvantageous because of the extra sealant which must be used and the increased difficulty in removing the seal by the consumer due to the additional adhesive sealant.
Prior tubular containers having a liner without an anaconda fold seam include the container disclosed in U.S. Pat. No. 3,520,463 to Ahlemeyer. The container disclosed therein includes a liner ply of aluminum foil which is coated on one surface to inhibit chemical attack. The liner ply web is fed to a pair of combining rolls where its uncoated surface is forced into contact with an adhesively coated surface of a body ply web. Solvent based adhesives are disclosed and include animal glue, casein-latex emulsion, vinyl-copolymer emulsion, and sodium silicate. The composite web is then spirally wound into tubular form about a mandrel to create a continuous tube. The overlapping edges of the liner ply are secured together with a hot melt adhesive.
A method of making wound tubular products without a water based adhesive is disclosed in U.S. Pat. No. 3,524,779 to Masters, et al. The method includes winding an inner ply made of a metal foil onto a shaping mandrel. An outer ply is then wound onto the mandrel from the opposite direction. A thermoplastic resin adhesive is precoated on the outer ply and optionally on the inner ply, and the outer ply is heated as it approaches the mandrel to activate the adhesive. A winding belt then firmly presses the plies together to obtain a solid container wall. As noted above, the metal foil provides a relatively stiff inner ply which allows the liner to be wound independently on the mandrel but which adds extra expense and thickness to the container construction.
U.S. Pat. No. 4,717,374 to Elias and assigned to the assignee of the present invention discloses a method for forming a composite container with a high barrier liner layer. The liner layer includes a metal layer of aluminum which is vacuum deposited on a resinous base film made of oriented polyethylene terephthalate. The liner also includes a second resinous layer opposite the first so as to form a sandwich around the metallized layer. On the exposed surfaces of the first and second resinous films are surface layers of copolyester which are heat seal compatible with each other so that the liner can be sealed to itself along the seam.
The Elias patent notes that the surface layer adjacent to the product must have sufficient mobility over a winding mandrel to allow the tubes to be wound and that the opposite surface is adhered to the inner ply of the paperboard layer by any of the then known techniques. The liner is heated only along an edge thereof as the liner is wound onto the mandrel so that the heated edge is heat sealed to the opposite edge of the preceding convolution. Heating more than the edge would cause the liner to adhere to the mandrel. The paperboard layer and label layer are then wound over the edge-sealed liner layer. Although the Elias patent discloses an exemplary liner, conventional techniques are disclosed for adhering the liner to the paperboard ply and as such include the added steps of separately applying an adhesive and/or precoating the paperboard with some type of adhesive or adherable surface to allow the liner ply to the adhered thereto.
Accordingly, it would be desirable to provide methods and apparatus for manufacturing a tubular container having an unsupported liner ply which does not include a foil layer and which could be sealed without using an anaconda fold seam. In addition, it would be highly desirable to provide such a container wherein the liner ply is securely adhered to the body ply without the separate application of a solvent based or water based adhesive and without precoating the inner surface of the body ply. It would be especially desirable if these objects and advantages could be combined in the same container.